Participants are 50 to 90 years of age, but almost all are 60 and older. They have been enrolled as volunteers from communities in Mission Park, Boston, and Steubenville. Inclusion criteria includes the ability to walk on level ground. Exclusion criteria includes unstable anginal, and baseline EKG patterns such as left bundle branch block that would make difficult the detection of repolarization abnormalities. Participants live at or near the study center which was located in an office or apartment in the apartment building of the majority of the participants.